Neville Loves . . . Luna?

Despite knowing that Neville will later marry Hannah Abbot and Luna will later marry Rolf Scamander as well as the fact that Neville and Luna remain strictly friends in the series, Harry Potter and the Deathly Hallows Part 2 still leaves the impression that Neville and Luna will be together because he has loved her for years. Then, at the end, there is an image of the two of them sitting next to one another reaffirming this impression as truth. 

The question is, then, why did the film writers choose to make this pairing and why did Ms. Rowling choose to let this pairing happen despite the fact that she never envisioned them together?

One answer can be traced back to Shakespeare.  
     At the end of his comedies, there was generally a wedding to leave the play on a good note with a happy ending - a tradition that has been continued over the years that has evolved into what we now call Romantic Comedies.

I know that seems ridiculous because Harry Potter and the Deathly Hallows is a far cry from comedic; however, after finally defeating Voldemort, the book does take a drastic turn towards the positive, culminating at the Epilogue where all was well. 
     Why not have a few love connections?
          Of course there's Ron and Hermione -- a match that had been building up since they first met on the Hogwarts Express their first year.
          Then, there is also Harry and Ginny -- not much of a surprise there, but at least Ginny's dream came true. She got to marry the man she had been crushing on since she was 10 and Harry didn't have to be jealous of all the boys Ginny went out with during her time at Hogwarts.
          That leaves Neville and Luna, the final two members who complete the second trio, It seems natural then to pair them together because everyone deserves love and, for the people who have only seen the movies, Neville and Luna must become a couple to round out the series.
               (Harry, Ron, and Hermione = golden trio; Neville, Ginny, and Luna = second trio)

I'm sure there are other reasons for why Neville and Luna ended up together in the film, but this is the one that makes the most sense to me, so I'm going to stick with that explanation. 

So there.